Rx headroom adjustment for stability improvement in wireless power systems

ABSTRACT

A wireless power system includes a receiver. The receiver may include a rectifier coupled to a receiver coil to receive power. The receiver may include a detector coupled to the rectifier to receive a monitor signal from the rectifier. The detector may provide a range signal indicating whether the monitor signal is outside a predetermined range. The receiver further includes an oscillation determiner coupled to the detector to receive the range signal. The oscillation determiner may determine that the rectifier is in an oscillation mode or is not in an oscillation mode. In some embodiments a communication unit is coupled to the oscillation determiner. The oscillation determiner may communicate a power adjustment signal and may request increased power through the communication unit.

TECHNICAL FIELD

Embodiments of the present invention are related to wireless powersystems and, specifically, to stability of wireless power receivers.

DISCUSSION OF RELATED ART

Mobile devices, for example smart phones and tablets, are increasinglyusing wireless power charging systems. Strong communication pulsesbetween the transmitter and receiver, however, can cause oscillations atthe receiver for some load levels. Such oscillation can appear atdifferent load levels based on alignment and other system parameters,load steps, or rising or falling loads. The oscillations can causeoutput instability and may reduce system efficiency.

Wireless power systems are much more efficient when the voltagedifference between the rectifier output voltage and power system outputvoltage is small. However, with that small difference communicationpulses and load variations may cause the power receiver system to settleat a point where the rectifier voltage goes into oscillation due tocurrent flow direction through the rectifier and voltage changes on thereceiver LC tank.

Therefore, there is a need to develop a scheme to prevent theoscillations.

SUMMARY

Embodiments of the present disclosure provide schemes for stoppingoscillation at a receiver of a wireless power system. A device such as adetector may be incorporated in the receiver of the wireless powersystem such that the device can determine the oscillation state of thereceiver and can generate a signal identifying the oscillation state ofthe receiver. The generated signal can be used by the wireless powersystem to stop the oscillations.

In accordance with aspects of the disclosure a receiver of a wirelesspower system is presented. The receiver includes a rectifier that iscoupled to the receiver and may receive power from a receiver coil. Thereceiver also includes a detector coupled to the rectifier to receive amonitor signal from the rectifier and provide a range signal indicatingwhether the monitor signal is outside a predetermined range. Thereceiver further includes an oscillation determiner coupled to thedetector to receive the range signal from the detector. The oscillationdeterminer may determine that the rectifier is in an oscillation mode oris not in an oscillation mode. The oscillation mode can be determinedbased on the range signal.

The receiver includes a rectifier and a detector coupled to therectifier. The detector may monitor a current and a voltage of therectifier. The receiver further includes an oscillation determinercoupled to the detector and to receive the monitored values of voltageand current of the rectifier. The oscillation determiner may determinean oscillation state of the rectifier and in response to thedetermination may generate one or more power adjustment signals. Thepower adjustment signals to be used by the transmitter for stopping anoscillation of the rectifier.

In some embodiments, a method of oscillation control of a receiver of awireless power system is provided. The method includes repeating thesteps of: i) monitoring an oscillation state of the receiver and ii) inresponse to determining the receiver is oscillating, transmitting apower adjustment signal to request increasing the power received by thereceiver, until determining the receiver stops oscillating. The methodfurther includes: in response to determining the receiver is notoscillating, repeating the steps of: i) transmitting a power adjustmentsignal to request decreasing the power received by the receiver; and ii)monitoring an oscillation state of the receiver, until the receiverstarts oscillating. The method further includes identifying the powertransmitted to the receiver when the receiver starts oscillating as anoscillation threshold of the receiver and transmitting a poweradjustment signal to request increasing the power received by thereceiver by a predefined headroom. The predefined headroom may move theoscillation state of the receiver away from the oscillation thresholdinto the non-oscillating state. The method also includes waiting for apredetermined amount of time for stabilizing the receiver.

Additional aspects, features, and advantages of the present disclosurewill become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless power transmission system.

FIG. 2 illustrates a receiver of a wireless power transmission systemthat can be used in the transmission system illustrated in FIG. 1.

FIG. 3 illustrates a wireless power transmission system according tosome embodiments that includes an oscillation determiner.

FIG. 4A illustrates an oscillation detector and a determination unit ofa receiver of a wireless power transmission system according to someembodiments.

FIG. 4B illustrates an oscillation example in a voltage or a current ofa rectifier of the receiver.

FIG. 5 illustrates a wireless power transmission system according tosome embodiments that includes a processor for oscillationdetermination.

FIG. 6A illustrate measurement results during operation of the wirelesspower transmission system according to some embodiments that does notinclude oscillation control.

FIG. 6B illustrate measurement results during operation of the wirelesspower transmission system according to some embodiments that includesoscillation control.

FIG. 7 is a flow diagram of a method of oscillation control of areceiver of a wireless power transmission system, according to aspectsof the present disclosure.

FIG. 8A illustrate measurement results during operation of the wirelesspower transmission system according to some embodiments that does notinclude oscillation control.

FIG. 8B illustrate measurement results during operation of the wirelesspower transmission system according to some embodiments that includesoscillation control.

FIG. 9A illustrate measurement results during operation of the wirelesspower transmission system according to some embodiments that does notinclude oscillation control.

FIG. 9B illustrate measurement results during operation of the wirelesspower transmission system according to some embodiments that includesoscillation control.

FIG. 10A illustrate measurement results during operation of the wirelesspower transmission system according to some embodiments that includesoscillation control.

FIG. 10B illustrate measurement results during operation of the wirelesspower transmission system according to some embodiments that includesoscillation control.

DETAILED DESCRIPTION

In the following description, specific details are set forth describingsome embodiments of the present invention. It will be apparent, however,to one skilled in the art that some embodiments may be practiced withoutsome or all of these specific details. The specific embodimentsdisclosed herein are meant to be illustrative but not limiting. Oneskilled in the art may realize other elements that, although notspecifically described here, are within the scope and the spirit of thisdisclosure.

This description and the accompanying drawings that illustrate inventiveaspects and embodiments should not be taken as limiting—the claimsdefine the protected invention. Various changes may be made withoutdeparting from the spirit and scope of this description and the claims.In some instances, well-known structures and techniques have not beenshown or described in detail in order not to obscure the invention.

Elements and their associated aspects that are described in detail withreference to one embodiment may, whenever practical, be included inother embodiments in which they are not specifically shown or described.For example, if an element is described in detail with reference to oneembodiment and is not described with reference to a second embodiment,the element may nevertheless be claimed as included in the secondembodiment.

FIG. 1 illustrates a system 100 for wireless transfer of power. Asillustrated in FIG. 1, a wireless power transmitter 102 drives a coil106 to produce a magnetic field. A power supply 104 provides power towireless power transmitter 102. Power supply 104 can be, for example, abattery based supply or may be powered by alternating current, forexample 120V at 60 Hz. Wireless power transmitter 102 drives coil 106at, typically, a range of frequencies, typically according to one of thewireless power standards.

There are multiple standards for wireless transmission of power,including the Alliance for Wireless Power (A4WP) standard and theWireless Power Consortium standard, the Qi Standard. Under the A4WPstandard, for example, up to 50 watts of power can be inductivelytransmitted to multiple charging devices in the vicinity of coil 106 ata power transmission frequency of around 6.78 MHz. Under the WirelessPower Consortium, the Qi specification, a resonant inductive couplingsystem is utilized to charge a device near the resonance frequency ofthe device. In the Qi standard, coil 108 is placed in close proximitywith coil 106 while in the A4WP standard, coil 108 is placed near coil106 along with other coils that belong to other charging devices. FIG. 1depicts a generalized wireless power system 100 that operates under anyof these standards.

As is further illustrated in FIG. 1, the magnetic field produced by coil106 induces a current in coil 108, which results in power being receivedin a receiver 110. Receiver 110 receives the power from coil 108 andprovides power to a load 112, which may be a battery charger and/orother components of a mobile device. Receiver 110 typically includesrectification to convert the received AC power to DC power for load 112.

FIG. 2 illustrates an example of a portion of receiver 110 illustratedin FIG. 1. As shown in FIG. 2, coil 108 is coupled through capacitor 202and capacitor 204 to a full-bridge rectifier circuit 220 formed by metaloxide semiconductor field effect transistors (MOSFETs) 206, 208, 210,and 212. AC power, illustrated as AC1 and AC2, received by coil 108 isrectified in the rectifier 220 to generate rectifier voltage Vrect. Thegates of transistors 206, 208, 210 and 212, labeled GH2, GH1, GL2, andGL1, respectively, are driven by a controller 214. Controller 214 candrive the gates of transistors 206, 208, 210, and 212 to optimize thedelivery of power at coil 108 and the transfer of rectified power toload 112. In some embodiments, the output from rectifier 220, thevoltage labeled Vrect in FIG. 2, may be further filtered and processedprior to assertion across load 112. Vrect can be placed on a power linewhile transistors 210 and 212 are coupled to a ground line. One skilledin the art will recognize that, although a full-bridge rectifier 220 isillustrated in FIG. 2, other embodiments may include a half-bridgerectifier. Further, rectifier 220 may be formed completely or partiallyof diodes instead of controlled transistors such as transistors 206,208, 210, and 212.

Some embodiments of the present invention are illustrated using thecomponents of receiver 110. One skilled in the art will recognize howother receivers can be modified to provide further embodiments of theinvention. For example, receiver 110 may further include a DC-DC voltageregulator receiving voltage Vrect from the rectifier and providing powerto load 112.

The example of receiver 110 illustrated in FIG. 2 may be appropriate fora single standard of wireless power transmission. In general, eachstandard requires that coil 108 meet specifications specific to thatstandard. Embodiments of the present invention allow for operation withdifferent standards, for example, a first standard may operate at 6.78MHz and a second standard may operate at less than 200 KHz. No matterwhich standard is used or even when a multimode device implementingmultiple standards is used, embodiments presented herewith can be usedto stop oscillation of the receiver.

In some embodiments, small voltage differences between Vrect and theoutput voltage (needed for optimal efficiency), the communicationpulses, and load variations may cause the system to settle at a pointwhere Vrect oscillates in voltage due to current flow direction throughthe rectifier and voltage changes on the Rx LC tank that need to becorrected.

In some embodiments, the wireless power system may oscillate duringoperation at different load levels based on alignment and other systemparameters (such as resonance values and Rx coil impedance), load steps,rising or falling loads. The oscillations may be considered as outputinstability and may reduce system efficiency or have any other negativeside effects or may have little impact other than being an undesiredoscillation.

The oscillations of the receiver can be prevented and the receiver canbe stabilized by increasing the rectifier voltage which can result inloss of efficiency. Also, the receiver can be stabilized by usingresonance capacitors with higher values and appropriate receiver coilsto dampen the oscillations, which can however cause efficiency loss atsome levels.

In accordance with some embodiments, a technique to stop theoscillations of the wireless power system while keeping efficiency highis introduced. When oscillation is detected, transmitter power can beincreased, increasing Vrect, until the oscillation goes away. In someembodiments, Vrect can then be slowly reduced until oscillation returns,saving the setpoint where oscillation appears, then increased again toabove the setpoint. In some embodiments, a headroom can be set bysetting the voltage Vrect to a headroom voltage above the setpoint.

In some examples, when the load current changes, the Vrect target againmay change and, if oscillation returns, the control loop can adjust forthe oscillations at a new set-point. However, if the oscillations do notappear, the power transmission level may not change and Vrect may beleft as it was.

FIG. 3 illustrates a wireless power transmission system 300 according tosome embodiments. Wireless transmission system 300 that includes adetector 322 And an oscillation determiner 317. As shown in system 300,a receiver circuit 302 receives the power from coil 306. The receiver302 includes capacitor 310 and capacitor 308 that couple the coil 306 toa rectifier 318. As such, rectifier 318 receives power from the coil 306and outputs rectifier voltage Vrect. Rectifier 318 may be a full-wave orhalf-wave rectifier. System 300 also includes a wireless powertransmitter 304 that drives a coil 312 to produce a magnetic field thatcouples the coil 312 to the coil 306.

As is further illustrated in system 300, detector 322 is coupled throughlinks 324 and 326 to the rectifier such that the detector 322 mayreceive the rectifier voltage Vrect signal through the link 324 and acurrent from rectifier 318 through link 326. In some embodiments,detector 322 receives one of the rectifier voltage Vrect or therectifier current and in some embodiments detector 322 receives both therectifier voltage Vrect and the rectifier current.

In some examples, rectifier 318 can be any rectifier. Rectifier 318 canbe a full-wave rectifier, half-wave rectifier, and may be formed withdiodes, transistors, or a combination of diodes and transistors.Further, rectifier 318 may be coupled to a power circuit that producesfiltering and DC-DC conversion circuits in order to produce the circuitoutput voltage Vout.

In some embodiments, the rectifier 318 is consistent with the rectifier220 of FIG. 2 that also includes the controller 214 and the rectifiercurrent associated with the rectifier is a current of one of thetransistors (MOSFETs) 206, 208, 210, and 212. In some examples, acapacitor 320 can be coupled between Vrect and ground 303.

In some embodiments, detector 322 monitors the received rectifiervoltage signal and the rectifier current signal through the links 324and 326 to monitor the rectifier voltage and/or the rectifier current.Detector 322 determines whether a monitor voltage (the rectifier voltageVrect or a voltage indicating rectifier current) is swinging outside ofa predefined range around a median value. Detector 322, in someembodiments, may generate a signal indicating each time the monitoredvalue or values is outside the predefined range.

System 300 further includes an oscillation determiner 317. In someexamples, the oscillation determiner 317 is coupled through a link 328to the detector 322 and receives signals from detector 322 thatindicates whether the monitored voltage is outside the predefined range.In some examples, the oscillation determiner 317 determines whether therectifier 318 is oscillating. An example of the operation of theoscillation determiner 317 with detector 322 is described in moredetails with respect of FIG. 4A. In some examples, the oscillationdeterminer 317 sets the oscillation state of the rectifier asnon-oscillating when it identifies that neither the rectifier voltagesignal nor the rectifier current signal is oscillating. In someexamples, the oscillation determiner 317 sets the oscillation state ofthe rectifier to oscillating when it identifies an oscillation on one ofthe rectifier voltage signal or the rectifier current signal.

In some embodiments, the oscillation of the rectifier voltage signal isdetermined by the oscillation determiner 317 when the rectifier voltageswings outside of a voltage interval around Vrect of greater than thepredetermined value for a predetermined number of times in a particularinterval of time. An oscillation in voltage or current of the rectifieris illustrated with respect to FIG. 4B. In some examples, the voltageinterval can be at least 50 millivolts, the predetermined number oftimes can be at least 10 times, and the particular interval of time isat most 1 second. In some examples, if the Vrect voltage is attempted tobe programmed to 5.25V, but the oscillation detector determines that thevoltage is varying from 5.35 V to 5.15 V at a repetitive frequency,which could be a frequency other than the operating frequency of thewireless power system or any other repetitive interval of time, theoscillation detector will signal the processor that an oscillation isdetected due to the target Vrect voltage exceeding the ±50 mV allowablethreshold.

In some embodiments, the oscillation of the rectifier current signal isdetermined by the oscillation determiner 317 when the rectifier currentswings outside of a current interval of greater than a predeterminedcurrent for another predetermined number of times in another particularinterval of time. In some examples, the current interval can be at least20 milliamps, the predetermined number of times is at least 5 times, andthe particular interval of times is at most 1 second. In some examples,in stable operation, the output current should be equal to the currentassociated with Vrect to within ±10 mA. In some examples, if the ‘LOADoutput current’ is currently 250 mA and then if the Vrect sensed currentis different from the ‘LOAD output current’ by +25 mA and then by −25 mAand repeating; the oscillation detector determines that the Vrectcurrent is varying from 275 mA to 225 mA at repetitive frequency, whichcan be a frequency other than the operating frequency of the wirelesspower system or any other repetitive interval of time, the oscillationdetector will signal the processor that an oscillation is detected dueto the ‘LOAD output current’ being constant to within allowable 20 mAwhile the Vrect current is exceeding the ±20 mA allowable threshold.

System 300 further includes a communication unit 315 coupled tooscillation determiner 317. In some examples, the communication unit 315is coupled through a link 327 to the oscillation determiner 317 andreceives power adjustment signals from the oscillation determiner 317.In some examples, the communication unit 315 transmits the poweradjustment signals through a link, which may be a communication channel329, to the wireless power transmitter 304.

In some examples, the wireless link 329 can be a wireless communicationchannel between the receiver 302 and the transmitter 304. For example,link 329 can be a wireless channel such as Bluetooth. In someembodiments, communication unit 315 may use the wireless power link, forexample, data may be transmitted through the capacitive link betweentransmit coil 312 and receive coil 306. In some examples, thecommunication channel is an inductance link between a coil 306 of thereceiver 302 and a coil 312 of the transmitter 304. The controller 340of the transmitter 304 receives the power adjustment signals via thecoil 312 of the transmitter 304. In some embodiments, data may betransmitted by modification of the magnetic coupling between transmitcoil 312 and receive coil 306. In some examples, communications can beaffected using the capacitive coupling between coils 312 and 306 so asnot to use the magnetic coupling channel.

In some embodiments, the wireless power transmitter 304 includes acontroller 340 that receives the power adjustment signals through thewireless link 329. The power adjustment signals from the receiver mayrequest the transmitter to adjust a level of power transmitted from thetransmitter. In some examples, the wireless power transmitter 304adjusts the power transmitted to the coil 312 based on the receivedpower adjustment signals. In some examples, the wireless powertransmitter 304 increases the power transmitted to the coil 312 and thusincreases the power received by the receiver coil 306 which in returnincreases the rectifier voltage Vrect. In some other examples, thewireless power transmitter 304 decreases the power transmitted to thecoil 312 and thus decreases the power received by the receiver coil 306which in return decreases the rectifier voltage Vrect.

The increase or decrease of the voltage supplied to rectifier 318modifies the oscillation state of the rectifier 318 between oscillatingand non-oscillating. In some examples, the power adjustment signal mayinclude an indication to increase or decrease the power transmissionlevel from the transmitter to the receiver by step functions of apredefined amount. In some examples, the power adjustment signal mayinclude an amount the power transmission level from the transmitter tothe receiver may be increases or decreased.

FIG. 5 illustrates a wireless power transmission system 500 according tosome embodiments. In system 500, the functions of detector 322 andoscillation determiner 317 are formed by a processor 522. Processor 522can be any processor system that can execute instructions. Processor 522may include both volatile and non-volatile memory as well asmicro-computers or other processing devices. In general, processor 522can execute instructions stored in its memory.

As shown in FIG. 5, receiver 302 includes a first analog-to-digitalconverter (ADC) 535 coupled through the link 324 to the rectifier 318 asecond ADC 530 coupled through the link 326 to the rectifier 318.Processor 522 is coupled to the first and the second ADC through thelinks 534 and 532 respectively. In some examples, the detector 522together with the ADCs 530 and 535 may perform the functionality of bothdetector 322 and oscillation determination 317 of FIG. 3.

In some examples, the ADC 535 receives the rectifier voltage signalthrough the link 324, digitizes the rectifier voltage and sends thedigitized rectifier voltage through the link 534 to the processor 522.Also, the ADC 530 receives the rectifier current signal through the link326, digitizes the rectifier current and sends the digitized rectifiercurrent through the link 532 to the processor 522. In some examples, theprocessor 522 may receive one of the monitored signals, the quantizedrectifier voltage or rectifier current. In some examples, the processorreceived both of the monitored signals.

In some examples, the processor 522 constantly monitors the receiveddigitized rectifier current and the digitized rectifier voltage anddetermines whether the monitored signals are oscillating. If theprocessor 522 determines an oscillation, the processor 522 provides apower adjustment signal through the link 327 to the communication unit315. In some examples, the processor determines an oscillation byidentifying the number of times the monitored signals have crossed athreshold.

FIG. 4A illustrates an algorithm 405 that may be performed by detector322 and oscillation determiner 317 or by processor 522. In step 410, amonitored signal, which may be the rectifier voltage Vrect and/or therectifier current, is received. In step 440, which may be performed bydetector 322, algorithm 405 determines whether the monitored signal isoutside of a predetermined range. The determination of being outside thepredetermined range is illustrated with respect to FIG. 4B. Asillustrated in FIG. 4B, monitored signal 495 varies around a mean value492. Step 440 determines that monitored signal 495 is outside thepredetermined range 490 if its maximum and minimum value lies outside ofthe predetermined range 490.

If algorithm 440 determines, in step 440, that the monitored signal 495is outside the predetermined range 490, then a counter is incremented inincrement counter step 460. In step 430, algorithm 405 determineswhether or not the value of the counter incremented in step 460 isgreater than a maximum value. Algorithm 405 determines that rectifier318 is in an oscillation state when the number of the incrementalcounter exceeds a predetermined Max Value. As illustrated in FIG. 4A, ifthe Max Value is exceeded, then algorithm 405 proceeds to step 470 wherea request to increase the power is transmitted to the transmitter, asdiscussed above. From step 470, algorithm 405 resets the counter in step420 and returns to step 410.

If, in step 440, it is decided that the monitor signal is not outsidethe predetermined range or, in step 430, it is decided that the counterhas not exceeded the Max Value, the algorithm 405 proceeds to step 450.In step 450, algorithm 405 determines whether a set amount of time haspassed. If the set amount of time has passed, then the counter and timerare reset in step 420 and algorithm 405 returns to step 410. If the setamount of time has not passed, then algorithm 405 returns to step 410.

In this fashion, receiver 302 in system 300 or system 500 determineswhether rectifier 318 is in an oscillating state or not in anoscillating state. If, as illustrated in algorithm 405, receiver 302determines that an oscillating state exists, then receiver 302 canrequest transmitter 304 to increase its power output in order toincrease the rectifier voltage Vrect until receiver 302 determines thatit is in a not oscillating state.

FIG. 4B illustrates an oscillation example in the monitored signal,which as discussed above may be the rectifier voltage Vrect or therectifier current of rectifier 318 of receiver 302. The graph 400 showsan oscillation 495 around a median value 492. In some examples, when therectifier voltage Vrect 492 swings outside of a voltage interval aroundmedian Vrect 492 that exceeds a predetermined range 490 for apredetermined number of times in a particular interval of time 498, thenstep 440 of algorithm 405 determines that rectifier 318 is oscillating.In another example, when the rectifier current 492 swings outside of acurrent interval 492 of greater than a predetermined value 490 for apredetermined number of times in a particular interval of time 498, thenstep 440 of algorithm 405 determines that rectifier 318 may beoscillating. In some examples, it is determined that the monitoredsignal of rectifier 318 are outside a predetermined range 490 when themonitored system cross both the lower and the upper thresholds 491 and493 respectively for a predetermined number of times within apredetermined time frame. The predetermined number of times can be anynumber, for example a number in the range of 3 to 10, while thepredetermined time frame may be up to several seconds; however, thedetermination can typically be made within 10 ms or by 25 times crossingthe threshold range. In some examples, the value 492 is an average ofthe monitored signal or is a programmed target value and the range 490is defined around the value 492.

In some examples, the monitored signal of rectifier 318 may change overtime, and the median may drift. The changes can be consideredoscillation when they follow an oscillation pattern as described above.For example, if the current or voltage of the rectifier changes with adetectable frequency and a particular amplitude, then it can beconsidered an oscillation. In another example, since noise exists, smallchanges do not qualify as oscillation and the changes may haverecognizable and repetitive amplitudes to be recognized as oscillation.Thus, the oscillations may have a frequency and amplitude that aredefined in predefined ranges.

Referring back to FIG. 5, system 500 may further include an inductionunit 510 coupled to the communication unit 315. The communication unit315 transmits requests 512 for power adjustment, the power adjustmentsignals, through the induction unit 510, the receiver coil 306, and thetransmitter coil 312 to the controller 340 of the wireless powertransmitter 304. The induction unit 510 couples the power adjustmentsignal to the receiver coil 306 and then power adjustment signal istransmitted through the magnetic field that couples the coil 312 to thecoil 306 to the transmitter 304 where the controller 340 may receive thepower adjustment signal via a coupling to the coil 312. In someexamples, the induction unit 510 couples the power adjustment signalthrough a separate coil to the receiver coil 306. In some otherexamples, the induction unit 510 induces a current change in thereceiver coil 306 at a frequency distinct from the frequency of theoperation of the wireless power system. In some examples, a load 520 iscoupled between the output of the rectifier Vrect and the ground 303. Insome examples, other communication methods may also be employed, such asBluetooth communication signals.

Referring back to FIG. 3, in some examples, the wireless power system300 may include the induction unit 510 coupled to the receiver coil 306such that the communication unit 315 may transmit the power adjustmentsignal through the induction unit 510, the receiver coil 306, and thetransmitter coil 312 to the wireless power transmitter 304.

FIGS. 6A, 6B, 8A, 8B, 9A, 9B, 10A, and 10B, that are each associatedwith some embodiments are described below. The figures show someoscillation examples and the examples of applying the systems 300 ofFIG. 3 or system 500 of FIG. 5 to control the oscillations.

FIG. 6A illustrates measurement results during operation of an examplewireless power transmission system that does not include oscillationcontrol. As shown in the graph 600, the rectifier voltage Vrectoscillates when output current Tout is essentially fixed. Also, thegraph 600 shows that output voltage of the receiver includes effects,e.g., traces, of these oscillations.

FIG. 6B illustrates measurement results during operation of the wirelesspower transmission system according to some embodiments that includesoscillation control. As shown in the graph 650, the rectifier voltageVrect oscillates for short intervals of time until the oscillation isstopped. As shown the output current Tout is essentially fixed. Also,the graph shows that output voltage of the receiver includes effects,e.g., traces, of the oscillations in the same short intervals of timeuntil the oscillation control stops the oscillations.

FIG. 8A illustrates measurement results during operation of the wirelesspower transmission system according to some embodiments that does notinclude oscillation control. As shown in the graph 800, the rectifiervoltage Vrect oscillates. Also, the graph shows that output voltage Voutof the receiver may include effects, e.g., traces, of theseoscillations. As shown, in some examples, the oscillations 810 beginwhen the output current Iout 820 jumps up.

FIG. 8B illustrates measurement results during operation of the wirelesspower transmission system according to some embodiments that includesoscillation control. As shown in the graph 850, the rectifier voltageVrect oscillates for short intervals of time until the oscillation isstopped. Also, the graph 850 shows that output voltage Vout of thereceiver may include effects, e.g., traces, of these oscillations. Asshown, in some examples, a slow ramp may occur for a short interval 870when the output (load) current Iout 860 jumps up or Iout 865 jumps downand then stops due to implementing the oscillation control. In someexamples, an upward or a downward sharp jumps 875 may occur before theslow ramp 870.

FIG. 9A illustrates measurement results during operation of the wirelesspower transmission system according to some embodiments that does notinclude oscillation control. As shown in the graph 900, the rectifiervoltage Vrect oscillates in multiple places 920 when the output currentTout 920 gradually changes, e.g., in 10 seconds, from 0 amp to 1 ampthen back to 0 amp. Also, the graph shows that output voltage Vout ofthe receiver may include effects, e.g., traces, of these oscillations.

FIG. 9B illustrates measurement results during operation of the wirelesspower transmission system according to some embodiments that includesoscillation control. As shown in the graph 950, when the output currentIout 960 gradually changes, e.g., in 10 seconds, from 0 amp to 1 ampthen back to 0 amp, the rectifier voltage Vrect shows a more stabilizedbehavior because it may oscillate in multiple places for very shortintervals of time 975 and then stops. Also, the graph 950 may not showeffects, e.g., traces, of these oscillations in the output voltage Vout.

FIG. 10A illustrates measurement results during operation of thewireless power transmission system according to some embodiments thatincludes oscillation control. In some examples, as shown in the graph1000, when the output current jumps up and the Vrect starts oscillating,the Vrect may be increased to stop the oscillations. In some examples,after stopping the oscillations at point 1020, the Vrect may slowlydecrease. The slow decrease of Vrect may be caused by slow increase inoutput current, e.g., load current. In some other examples, the slowdecrease in Vrect may be caused by decreasing the power transmissionfrom transmitter and may be performed to find the oscillation threshold.

FIG. 10B illustrates measurement results during operation of thewireless power transmission system according to some embodiments thatincludes oscillation control. In some examples, as shown in the graph1050, when the output current jumps down the Vrect may startsoscillating at point 1070. Then Vrect may be increased to stop theoscillations at point 1080. In some examples, after stopping theoscillations at point 1080, the Vrect may slowly decrease. The slowdecrease of Vrect may be caused by slow increase in output current,e.g., load current.

In some examples, when the receiver 302, and rectifier 318, are in anoscillating mode, the rectifier voltage Vrect can be increased above athreshold for onset of the oscillation mode of the rectifier/receiver inorder to cause receiver 302 to transfer to a not oscillating mode. Insome examples, the wireless power transmitter 304 increases the powertransmitted to the coil 312 by a predefined amount, which provides for aheadroom, above the threshold at which the rectifier stops oscillationto give a headroom for operation of the rectifier 318 above theoscillation threshold.

In some examples, adjusting the headroom and returning close to originalvalue will cause enough system change to alter the set-point into anon-oscillating point, even when the new setting is very close to theoriginal set-point that was oscillating.

In some other examples, increasing the headroom may cause continuedoscillations such that it can be corrected once the headroom is adequateenough. In some examples, a headroom of +0.5V above an oscillating pointmay still show oscillation, so Vrect is increase up another, e.g.,+0.25V (+0.75V total) to stop the oscillations. Then the headroom can bedecreased, however, the system may not exhibit the oscillations at thepreviously oscillating point, for example, when reducing Vrect to regainlost efficiency (due to increased Vrect), Vrect may be reduced by 0.6Vwithout introducing oscillations. In some examples, the oscillations mayexhibit certain degrees of hysteresis and as such, one may not assumethat lack of oscillation at an operating point, will always result in nooscillations at that specific operating point.

In some examples, when the receiver 302 is in a not-oscillating mode,the rectifier voltage Vrect can be decreased to determine the thresholdat which the oscillation of the rectifier/receiver may start. In someother examples, the threshold is the oscillation threshold. In someexamples, the wireless power transmitted to the coil 306 is increased bythe predefined amount over an oscillation threshold value in order tocreate the headroom above the threshold at which rectifier 318 startsoscillation. In some examples, the wireless power transmitter 304increases the power transmitted to the coil 312 by the predefined amountover the starting threshold voltage in order to create the headroomabove the threshold to move the rectifier to non-oscillating mode.

FIG. 7 is a flow diagram of a method 700 of oscillation control of areceiver 302 of a wireless power transmission system, according toaspects of the present disclosure. It is understood that the steps ofmethod 700 may be performed in a different order than shown in FIG. 7,additional steps can be provided before, during, and after the steps,and/or some of the steps described can be replaced or eliminated inother embodiments. The steps of method 700 can be considered as tasksand can be carried out by the power transmission systems 300 or 500 ofFIGS. 3 and 5, respectively. In some examples, the steps of method 700are performed in response to receiving the power adjustment signalsindicating a receiver is oscillating.

At step 702, the method 700 includes monitoring an oscillation state ofa receiver and to determine the oscillation state of a receiver asoscillating or non-oscillating. The determination can be performed bythe oscillation determiner 317 shown in diagrams 300, or the processor522 as shown in diagram 500, and according to aspects of algorithm 405as illustrated FIG. 4A.

If, in step 702, an oscillating state is detected, then method 700proceeds to step 704. At step 704, the method 700 includes generating apower adjustment signal to be transmitted to transmitter 304 to increasethe power received by receiver 302. As described herein and shown inFIGS. 3 and 5, the power adjustment signals in step 704 are generated bythe oscillation determiner 317 of the wireless power system 300 or theprocessor 522 of the wireless power system 500, as described above. Thesteps 702 and 704 may be repeated until the receiver is no longeroscillating.

In some examples, the oscillation state of the rectifier 318 of thereceiver 302 is determined as oscillating when at least one of thecurrent or voltage of the rectifier 318 is determined to be oscillating.In some examples, increasing the power transmission from the transmitter304 to the receiver 302 increases the voltage of the rectifier 318 suchthat by increasing the rectifier voltage the rectifier 318 may stoposcillating.

When step 702 of method 700 determines that there is no oscillation,then method 700 proceeds to step 706. At step 706, the method 700includes generating a power adjustment signal to decrease powertransmission from transmitter 304 received by receiver 302. In someexamples, the power adjustment signal to decrease power transmission toreceiver 302 may be generated after the first instance thereceiver/rectifier stops oscillation. In some embodiments the controller340 of the transmitter 304 may receive the power adjustment signal andmay command transmitter 304 to decrease power transmission. In someexamples, the controller 340 may command the transmitter to graduallydecrease the power transmission from the transmitter 304 to the receiver302. In some examples, decreasing the power transmission from thetransmitter 304 to the receiver 302 decreases the rectifier voltageVrect of the rectifier 318 such that by decreasing the rectifier voltagethe rectifier 318 may start oscillating.

At step 708, the method 700 includes monitoring the oscillation state ofthe receiver and to determine the oscillation state of receiver 302 asoscillating or non-oscillating. After sending a power adjustment signalto decrease the power transmission level, the oscillation determinationsunit 317 or processor 522 may monitor the oscillation state of thereceiver until a second instance that the oscillation state changes fromnon-oscillating to oscillating. In some examples, the steps 706 and 708may repeat until the receiver starts oscillating. In some examples, theoscillating state of receiver 302 is continuously monitored. In someexamples, the second instance that the oscillation state changes fromnon-oscillating to oscillating may be the oscillation threshold asdiscussed above.

In some other examples, the power transmission level from thetransmitter 304 to receiver 302 is gradually increased or decreased suchthat the oscillation determinations unit 317 or the processor 522 canclosely monitor the oscillation state of the receiver based on the poweradjustment signals.

Once oscillation has begun as indicated in step 708, method 700 proceedsto step 710. At step 710, method 700 includes identifying theoscillation threshold according to the current power level oftransmitter 304. In some examples the second instance when thereceiver/rectifier starts oscillating is noted. The power transmissionlevel received by receiver 304 at the second instance can be noted asthe oscillation threshold of the receiver.

At step 712, the method 700 includes generating a power adjustmentsignal for the transmitter to increase power transmission level receivedby the receiver with a headroom according to the threshold value plusthe predefined amount. In some examples, the oscillation threshold maynot be stable and thus the power transmission level received by thereceiver is slightly increased by the predefined amount to create theheadroom above the threshold of oscillation into the non-oscillatingstate.

At step 714, the method 700 may include waiting for a predeterminedamount of time until the receiver stabilizes. In some examples, theprocessor 522 or the oscillation determinations unit 317 may waitbetween 5 to 60 seconds, for example, 10 seconds such that the receiverstabilizes. At the end of the waiting period in step 714, method 700returns to step 702 to repeat the above steps.

The above detailed description is provided to illustrate specificembodiments of the present invention and is not intended to be limiting.Numerous variations and modifications within the scope of the presentinvention are possible. The present invention is set forth in thefollowing claims.

What is claimed is:
 1. A wireless receiver, comprising: a rectifier configured to receive power from a receiver coil; a detector configured to receive a monitor signal from the rectifier and provide a range signal indicating whether the monitor signal is outside a predetermined range; an oscillation determiner configured to receive the range signal from the detector, the oscillation determiner is configured to determine whether a rectifier mode is an oscillation mode or is not in oscillation mode, to generate power-level adjustments for a wireless power transmitter that provides power to the receiver coil based on the rectifier mode, to determine a minimum operating power level below which the rectifier mode is in the oscillating mode by repeatedly providing power-level adjustments to reduce power until the rectifier mode is in the oscillation mode and identifying the minimum operating power level, and to determine an operating power level that is above the minimum operating power level; and a communication unit coupled to the oscillation determiner, the communication unit configured to communicate power-level adjustments to the wireless power transmitter.
 2. The wireless receiver of claim 1, wherein the detector is configured to compare the received monitor signal against an upper threshold and a lower threshold, and wherein the range signal indicating the monitor signal is outside the predetermined range is provided when the monitor signal crosses both the upper threshold and the lower threshold.
 3. The wireless receiver of claim 1, wherein the oscillation determiner is configured to determine the oscillation mode of the rectifier based on counting a number of times the range signal is outside the predetermined range.
 4. The wireless receiver of claim 3, wherein the counting is in a predetermined interval of time.
 5. The wireless receiver of claim 1, wherein the monitor signal is voltage or a current of the rectifier.
 6. The wireless receiver of claim 1, wherein the communication unit transmits the power adjustment signal to request for increased power through a wireless communication channel whenever the rectifier mode is the oscillation mode.
 7. The wireless receiver of claim 6, wherein the communication channel is an inductance link.
 8. The system of claim 1, wherein in response to the oscillation determiner determining an oscillation mode, the oscillation determiner of the receiver is configured to: repeating, until determining that the receiver is no longer in the oscillation mode: monitoring a state of the receiver to determine whether the receiver is in an oscillation mode; and in response to determining that the receiver is in the oscillation mode, transmitting a power adjustment signal to a transmitter to request increasing the power received by the receiver; in response to determining that the receiver is not in the oscillation mode, repeating until the receiver starts oscillating: transmitting a power adjustment signal to request decreasing the power received by the receiver; and monitoring the receiver to determine when it enters the oscillating mode; identifying the power transmitted to the receiver when the receiver starts oscillating in the oscillating mode as the minimum operating power level; and transmitting a power adjustment signal to request increasing the power received by the receiver by a predefined headroom, the predefined headroom is configured to move operation of the receiver away from an oscillation threshold where the receiver enters the oscillation mode into the non-oscillating state.
 9. The system of claim 8, wherein the monitor signal is determined as oscillating when the monitor signal swings outside an interval of greater than a first predetermined value for a first predetermined number of times in a first interval of time.
 10. A method of oscillation control of a receiver of a wireless power system, comprising: determining an oscillation state of the receiver; in response to determining that the receiver is oscillating, repeating, until determining the receiver stops oscillating: monitoring an oscillation state of the receiver; in response to determining the receiver is in an oscillating mode, transmitting a power adjustment signal to request increasing the power received by the receiver; in response to determining the receiver is not in the oscillating mode, repeating until the receiver enters the oscillating mode: transmitting a power adjustment signal to request decreasing the power received by the receiver; and monitoring the oscillation state of the receiver; identifying the power transmitted to the receiver when the receiver starts oscillating as an oscillation threshold of the receiver; once the oscillation threshold is identified, transmitting a power adjustment signal to request increasing the power received by the receiver by a predefined headroom above the oscillation threshold, the predefined headroom is configured to move the oscillation state of the receiver away from the oscillation threshold into the non-oscillating state; and waiting for a predetermined amount of time for stabilizing the receiver.
 11. A method of claim 10, further comprising: transmitting the power adjustment signal via a communication unit of the receiver and through wireless channels.
 12. A method of claim 10, wherein the receiver of the wireless power system includes a rectifier, and wherein the method further comprises: determining the oscillation state of the receiver based at least on the oscillation state of the rectifier; determining the oscillation state of the rectifier based at least on determining a current or a voltage of the rectifier as oscillating.
 13. The method of claim 12, further comprising: determining a voltage of the rectifier as oscillating when the rectifier voltage swings in a voltage interval of greater than a first predetermined value for a first number of times in a first interval of time; determining a current of the rectifier as oscillating when the rectifier current swings in a current interval of greater than a second predetermined value for a second number of times in a second interval of time.
 14. The method of claim 10, further comprising: receiving a monitor signal from a rectifier of the receiver; comparing the received monitor signal against an upper threshold and a lower threshold; generating a range signal when the monitor signal crosses both the upper threshold and the lower threshold. 